Hydraulic fracturing is a stimulation technique used to increase the production of hydrocarbons from subterranean formations. During hydraulic fracturing, a fracturing fluid and/or pad fluid is pumped into a subterranean formation at a rate and pressure sufficient to break down or erode the formation thereby initiating and/or propagating one or more hydraulic fractures. While pad fluids generally do not contain particulates, fracturing fluids typically carry and deposit solids, such as proppant, into the fracture. When properly deposited, proppant acts as a physical barrier to prevent the propped portions of the fractures from closing. After the completion of a hydraulic fracturing treatment, properly propped fractures provide a pathway for hydrocarbons and/or other formation fluids to flow into the wellbore. Unpropped fractures, on the other hand, close back allowing little, if any, fluid flow. Accordingly, the hydrocarbon production potential of a hydraulically fractured well depends upon the transport properties of the fracturing fluid—more particularly, the ability of the fracturing fluid to transport and deposit proppant along the full length and height of the fracture—as well as the conductivity of the propped fracture.
While traditional hydraulic fracturing operations rely on relatively high viscosity fracturing fluids (e.g., aqueous gels, oil-based fluids, viscoelastic surfactant gels, and emulsions) to transport proppants, current fracturing operations often utilize low-viscosity fracturing fluids (e.g., slickwater) to enhance the generation of complex fracture networks in unconventional formations such as shale. Additionally, the use of such low-viscosity fluids can reduce operational costs and formation damage. Unfortunately, low-viscosity fracturing fluids typically exhibit poor transport properties compared to relatively high viscosity fracturing fluids. Specifically, conventional proppants and/or proppant mixtures (e.g., frac sand) tend to settle out of low-viscosity fluids.
Proppant settling reduces the effective length and height of a propped fracture as well as the final conductivity of the propped fracture. In addition, when proppant settles, it prematurely drops out of solution leaving less proppant in the fracturing fluid, resulting in unpropped or under-propped fractures and reducing the effective length of the propped fracture. By depositing proppant preferentially on the bottom side of the fracture, settling also leaves much of the fracture's height unpropped, effectively reducing the height of the propped fracture. Like wholly unpropped fractures, the unpropped portions of a propped fracture are susceptible to complete or partial close back. Thus, by reducing the effective length and height of a propped fracture, settling can significantly reduce the fracture's conductivity. Moreover, as the unpropped portions of the fracture close, the settled proppant may be crushed under the fractures' closing stresses, thereby further diminishing the fracture conductivity and flow potential of any fluid flowing through the propped fracture.
Thus, there is a continuing need for hydraulic fracturing methods utilizing low-viscosity fluids that provide improved and/or additional connective flow paths through propped fractures.